Spindle head unit of a machining center

ABSTRACT

A spindle head unit having a bell crank lever (24) mounted pivotally on a spindle head (10) of a machining center to depress a drawbar (18) inserted through a spindle (14) mounted on the spindle head (10). One of arms of the bell crank lever (24) is located so as to be capable of being engaged with a guide cam (28) and a depressing end (24a) in the shape of a spherical protrusion which is not connected mechanically to an upper end (18a) of the drawbar (18) is formed in a free end of the other arm of the bell crank lever (24). The bell crank lever (24) is urged continuously by a spring means (32) so that the former arm is urged toward the guide cam (28).

This application is a continuation of application Ser. No. 709,949 filedFeb. 27,1985.

DESCRIPTION

1. Technical Field

The present invention relates to a spindle head unit of a machiningcenter equipped with an automatic tool changer, and more specifically,to a spindle head unit of a machining center having a simplified toolchanging mechanism employing a draw bar of the spindle whenautomatically changing tools between a tool magazine and the spindle.

2. Background Art

A machining center is equipped with an automatic tool changing devicehaving a tool magazine and carries out diversified machining processesautomatically and quickly by indexing a desired tool among a pluralityof tools mounted on the tool magazine, and then automatically changingthe tool which has been used on the spindle for the desired tool.Accordingly, a machining center, in general, is equipped with a spindlehead unit comprising, in combination, a spindle head and a tool changingmechanism for removing a tool which has been used from the spindle, andthen mounting a desired tool on the spindle for automatic tool changing.An example of a prior art embodiment of a machining center equipped withsuch a spindle head unit is shown in FIGS. 1 and 2.

Referring to FIGS. 1 and 2, this conventional machining center isequipped with a spindle head 3 supported on a column 2 above a worktable 1 for vertical movement, and the tool magazine 3a of an automatictool changing device is provided on the front side of the spindle head3. A plurality of tools T to be changed automatically are held on thetool magazine 3a. The spindle head 3 has a cylindrical spindle 4, adrawbar 5 disposed inside the spindle 4 for vertical movement, with theupper end projecting from the upper end of the spindle 4 and adapted tomake, in cooperation with the spindle 4, the lower end of the spindle 4clamp a desired tool T through upward movement relative to the spindle4, and to release a tool T which has been used from the lower end of thespindle 4 through downward movement relative to the spindle 4. A spring6 urges the drawbar 5 upward relative to the spindle 4, and a drawbardepressing lever 8 is pivotally mounted on the spindle head 3 so as toengage a cam 7 provided on the column 2 when the spindle head 3 israised to a predetermined height, and thereby is moved so as to depressthe drawbar 5. That is, the machining center is equipped with a spindlehead unit having the depressing lever 8 adapted to be controlled by thecam 7 fixed to the column 2 for swing motion about a pivotal axis, andadapted to drive the drawbar 5 for vertical motion to control the toolchanging operation. On the other hand, the spindle 4 is driven forrotation by a spindle driving motor, not shown, through a belt-pulleymechanism 4a.

In the above-mentioned conventional spindle head unit of a machiningcenter, the drawbar depressing lever 8 is connected to the drawbar 5through a connecting pin 9, and hence the drawbar 5 rotates togetherwith the spindle 4, because the spindle 4, the tool, and the drawbar 5are connected firmly together when the spindle 4 clamps the tool incooperation with the drawbar 5.

Accordingly, in such a conventional spindle head unit, a drawbar housing5b is mounted rotatably through bearings 5a on the upper end of thedrawbar 5 and joined to the drawbar depressing lever 8 by a pin 9. Thisconstitution requires a complex connecting mechanism for interlockingthe drawbar 5 and the drawbar depressing lever 8, and causes an increasein the number of parts and a deterioration in the facility of theassembling work. Furthermore, such a constitution suffers unavoidablyfrom vibrations in the connecting mechanism interconnecting the drawbar5 and the drawbar depressing lever and thus produces noise.

DISCLOSURE OF THE INVENTION

Accordingly, it is an object of the present invention to provide aspindle head unit of a machining center, by which those problems in theconventional spindle head unit of the prior art are eliminated.

The present invention provides a spindle head unit of a machiningcenter, comprising a spindle head supported for vertical movement abovea work table on a column, a cylindrical spindle held in the spindlehead, a drawbar disposed vertically and movably within the spindle withthe upper end thereof protruding upward from the spindle and arranged insuch a manner that a changeable tool is clamped in a lower end of thespindle through cooperation of the spindle and the drawbar when thedrawbar is raised relative to the spindle, and that a tool which hasbeen used is released from the lower end of the spindle when the drawbaris moved downward, a spring for urging the drawbar upward relatively tothe spindle, and a drawbar depressing lever pivotally mounted on thespindle head so as to engage a cam provided on the column when thespindle head is raised to a predetermined height, and thereby to beturned in a direction to depress the drawbar, characterized in that thedrawbar depressing lever is provided at one end thereof with adepressing means which is pressed against an upper end surface of thedrawbar to apply a downward pressure to the drawbar when the drawbardepressing lever is turned toward the drawbar by the cam, and thatanother spring is provided to urge the depressing means so that thedepressing means is separated from the upper end surface of the drawbarwhen the drawbar depressing lever is turned in the reverse direction bythe cam. In this constitution, it is preferable that the upper endsurface of the drawbar has the form of a flat pressure-receiving surfaceand the depressing means of the drawbar depressing lever is formed as aspherical protrusion at the end of the drawbar depressing lever.Furthermore, it is desirable that the latter spring is a compressionspring capable of urging one arm of the drawbar depressing lever formedas a bell crank lever toward the cam.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a machining center equipped with aconventional spindle head unit;

FIG. 2 is a sectional view of the essential part of the spindle headunit of FIG. 1;

FIG. 3 is a sectional view showing the essential part of a spindle headunit of a machining center, according to the present invention; and

FIG. 4 is a plan view of the essential part of the spindle head unit ofFIG. 3.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to FIGS. 3 and 4 which show a preferred embodiment of thepresent invention, a spindle head unit of a machining center has aspindle head 10 capable of moving vertically above a work table. Thespindle head 10 is supported on a machine body 12 by a supportingmechanism, not shown.

A cylindrical spindle 14 is supported vertically so as to rotate aboutthe center axis thereof on the spindle head 10. The spindle 14 is drivenfor rotation by a spindle driving motor, not shown in FIG. 3, through abelt-pulley device 14a. A tool receiving part 16 for receiving a toolsupplied by an automatic tool changer, not shown, is formed in the lowerend of the spindle 14. Although not shown herein, ordinarily, theautomatic tool changer has a tool transfer means for transferring a toolto a position directly below the spindle 14 and a tool magazine forholding a plurality of tools, however, the automatic tool changer may beof the type not having a tool transfer means, but having a tool magazinedisposed in front of the spindle head 10 in an inclined position andadapted to be rotated for indexing to locate a desired tool at aposition directly below the spindle 14.

The tool receiving part 16 of the spindle 14 is brought into engagementwith or disengaged from a tool through the vertical movement of thespindle head 10.

A drawbar 18 is provided so as to be vertically movable within thespindle 14 with an upper end surface 18a thereof projecting upward fromthe spindle 14.

In the tool receiving part 16, the drawbar 18 retains a plurality ofballs 20 for clamping a tool at a pull stud formed in the top end of thetool. When the drawbar 18 is moved upward relative to the spindle 14,the balls 20 are acted on by the inner surface of a reduced diameter ofthe tool receiving part 16 so as to be engaged with the pull stud of thetool so that the tool is firmly clamped in the lower end of the spindle14. When the drawbar 18 is moved downward relative to the spindle 14,the balls 20 are allowed to be disengaged from the pull stud of thetool, so that the tool is released from the lower end of the spindle 14.

A plurality of coned disk springs 22 for urging the drawbar 14 upwardrelative to the spindle 14 are provided between the inner periphery ofthe spindle 14 and the outer periphery of the drawbar 18 so that thedrawbar 18 is capable of being pushed up to a fixed height relative tothe spindle 14.

A drawbar depressing lever 24 is mounted pivotally by a horizontal shaft26 on the upper surface of the spindle head 10. A roller 30 which comesinto engagement with a cam 28 provided on the machine body 12 when thespindle head 10 is raised to a fixed height is provided on one end ofthe lever 24. The lever 24 has a pressing end 24a which depresses thedrawbar 18 at the upper end surface 18a relative to the spindle 14 whenthe roller 30 of the lever 24 is brought into engagement with the cam28. The depressing end 24a has a spherical surface facing the upper endsurface 18a of the drawbar 18.

A spring 32 for urging the lever 24, so that the depressing end 24a isseparated from the upper end surface 18a of the drawbar 18 while thelever 24 is not in engagement with the cam 28, is disposed between thespindle head 10 and the lever 24. A turn limiting bolt 32a for limitingthe turn of the lever 24 is disposed between the spindle head 10 and thelever 24. The turn limiting bolt 32a limits the excessive turn of thelever 24 on the horizontal shaft 26 due to the action of the spring 32when the lever 24 is disengaged from the cam 28.

In this embodiment, when changing the tool, the spindle head 10 israised together with a tool magazine, not shown, and thereby the roller30 of the lever 24 is moved along the surface of the cam 28, so that thedepressing end 24a of the lever 24 depresses the drawbar 18.Consequently, the tool is released from the tool receiving part 16 ofthe spindle 14. Then, the spindle head 10 is raised further relative tothe tool magazine to bring the lower end of the spindle 14 above thetool. In this state, the roller of the lever 30 is located above the cam28.

After the tool has been removed and another new tool has been indexed toa position directly below the spindle 14, the spindle head 10 islowered, and thereby the new tool is received in the tool receiving part16. With the downward movement of the spindle head 10, the roller 30 ofthe lever 24 rides on the cam 28 from above, and thereby the drawbar 18is depressed again. Consequently, the pull stud of the tool is receivedin the space between the balls 20 of the drawbar 18. After the roller 30of the lever 24 has been moved below the cam 28, the drawbar 18 isreleased from the depression of the lever 24. Consequently, the drawbar18 is forced to move upward relative to the spindle 14 by the resilientforce of the coned disk springs 22, and hence the balls 20 are engagedwith the neck of the tool and the spindle 14, and the tool and thedrawbar 18 are firmly connected together. That is, the tool is clampedin the lower end of the spindle 14.

Then, the spindle head 10 is lowered further together with the toolmagazine to the waiting position.

The spindle 14 is driven for rotation as it is lowered and the toolrotates together with the spindle 14. Since the drawbar 18 is connectedfirmly with the spindle 14 and the tool, the drawbar 18 rotates as thespindle 14 rotates. During the machining operation, since the roller 30of the lever 24 is not in engagement with the cam 28, the pressing end24a of the lever 24 is held apart from the upper end surface 18a of thedrawbar 18 by the resilient force of the spring 32. Accordingly, therotation of the drawbar 18 is not transmitted to the lever 24

Although the present invention has been described with reference to apreferred embodiment thereof, the present invention is not limitedthereto, but may be, for example, a spindle head unit having a toolclamping mechanism employing a collet. It will be obvious to thoseskilled in the art that various changes and modifications of the presentinvention are possible without departing from the scope of the appendedclaims.

The present invention simplifies the force transmitting mechanism fortransmitting the force of the drawbar depressing lever to the drawbar toa high degree, reduces the number of component parts, facilitates theassembling work, reduces the weight, and provides an automatic toolchanger with the least possibility of malfunction. Furthermore, themechanism according to the present invention produces less noise ascompared with the conventional mechanism, because the drawbar depressinglever is separated from the drawbar during the rotation of the spindle.

We claim:
 1. In a spindle head unit of a machining center of the typehaving a tool magazine for storing tools therein; a spindle headsupported for vertical movement along a column of the machining center,a spindle rotatably mounted in the spindle head and having atool-receiving end for receiving therein individual tools stored in thetool magazine, a draw-bar disposed for axial movement within the spindlebetween a tool-engaging position and a tool-disengaging position, thedraw-bar having one end engagable with a tool received in thetool-receiving end of the spindle when the draw-bar is at itstool-engaging position, the draw-bar having another end extendingaxially beyond the spindle, elastic pressure means continously urgingthe draw-bar towards its tool-engaging position, a draw-bar actuatingcam member fixed to the column and having an actuating surface, and abell-crank lever mounted at a corner thereof for pivotal movement abouta pivot mounted on the spindle head, the bell-crank having a cammember-engaging arm and a draw-bar-depressing arm, an end of thecam-member-engaging arm of the bell-crank lever being disposed forengagement with the cam member actuating surface upon upward movement ofthe spindle head so as to actuate the bell-crank lever to move about itspivot so that the draw-bar-depressing arm of the bell-crank leverdepresses the draw-bar toward the tool-disengaging position thereof, theimprovement comprising:an upper end surface member provided upon theother end of the drawbar; the drawbar-depressing-arm of the bell-cranklever being disposed above the upper end surface member of the draw-bar;a spherical depressing member directly attached at an under surface ofthe draw-bar-depressing arm of the bell-crank lever, for point contactwith the upper surface member of the draw-bar so as to depress thedraw-bar in response to arc movement of the draw-bar-depressing arm ofthe bell-crank lever by the cam member actuating surface; a springmember arranged between the spindle head and the bell-crank leveradjacent the pivot thereof for urging the bell-crank lever in adirection about the pivot thereof to separate the spherical depressingmember form the axially extended draw-bar end so as to hold apart thedraw-bar-depressing arm of the bell-crank lever from draw-bar while thebell-crank cam member-engaging end is disengaged from the cam memberactuating surface; and an adjustable limiting member disposed betweenthe spindle head and the bell-crank lever ajdacent the pivot thereof,for limiting excessive pivoting of the bell-crank lever under urging ofthe spring member when the bell-crank cam-engaging end is disengagedfrom the cama member actuating surface.
 2. The improved spindle headunit of claim 1, wherein an end surface of the axially extending end ofthe draw-bar is formed as a flat pressure-receiving surface, and thesperhical depressing member of the bell-crank lever draw-bar-depressingarm is a sperical protrusion surface provided on the draw-bar-depressingarm or the bell-crank lever.
 3. The improved spindle head unit of claim1, wherein the spring member is a compression spring urging the cammember-engaging end of the bell-crank lever toward the cam memberactuating surface.